In the synthetic-resin molding art and elsewhere in which hardenable or settable materials are to be used or applied, it is known to use a synthetic-resin system which consists of two mutually miscible and interreactive components which are combined in a mixing head to form the settable mixture, i.e. the synthetic-resin material.
For example, in the formation of polyurethane layers, bodies and the like, it is known to react polyol and di-isocyanate components in a mixing head to form a reactive mixture which can set. Either or both of these components can include an expanding or blowing agent so that the resulting body has a cellular or foamed characteristic.
In the formation of bodies from epoxy resins, the epoxy resin on the one hand and the amine hardener on the other hand can be mixed in a mixing head to form the settable mixture.
In general, the two components which are to be combined are fed to the mixing head in liquid form and can be displaced by respective metering pumps.
In German Pat. No. 2,065,841, French Pat. No. 71 05 304, in British Pat. No. 1,334,440 and in U.S. Pat. No. 3,706,515 (particularly FIG. 3) there is described a device for generating a chemically reactive mixture from at least two components capable of forming the ultimate synthetic-resin composition which comprises a mixing chamber whose walls are formed with orifices through which the individual components are fed. The mixing chamber has an outlet opening for the reactive component mixture and a control piston or plunger is reciprocable in the mixing chamber to block and unblock the orifices and drive residual mixture from the chamber in a certain cadence or time, depending upon the molding or other requirements. The plunger itself can be controlled by fluid-responsive means and is driven linearly between mixing and nonmixing positions.
In the system of these patents, when the plunger or control piston is in its mixing position, a baffle body is disposed in the mixing chamber in the region between the inlet opening or orifices and the outlet or discharge openings of the mixing chamber.
The block body or baffle barrier of the known device serves to generate a mixing prepressure in the mixing chamber and to influence the distribution of the jets or streams of the components so that mixing is promoted. When one or both of the components includes a blowing or expanding agent, this body makes it possible, by regulating the pressure in the mixing chamber (i.e. the mixing prepressure) to control the pore structure and the external appearance of any molded body formed with the mixture.
The baffle barrier formed by the aforementioned body is drawn into the wall of the mixing chamber and out of the path of the control piston when the latter is shifted from its mixing position to its nonmixing position, i.e. blocks the orifice and drives the residual mixture out of the mixing chamber. This system requires a separate control arrangement, including a piston and cylinder for the barrier body and makes a coordination between the several control elements mandatory if reliable operation is to be achieved.
German patent document (Auslegeschrift) No. 25 44 749 discloses an adjustable baffle barrier which can be set as to its spacing from the mixing chamber. However, since this baffle barrier is located downstream of the mixing chamber in a passage communicating with the mold, control in response to movement of the control piston is not possible. In this system as well hydraulic control of the adjustment of the baffle barrier is provided.
Frequently it is desirable to avoid any use of a passage between the mixing chamber and the mold and in this case the principles of the last-mentioned publication are inapplicable.